Modeling of filtration characteristics during submerged hollow fiber membrane microfiltration of yeast suspension under aeration condition

Comparative Study of Membrane Fouling with Aeration Shear Stress in Filtration of Different Substances

The formation process of membrane fouling is complex and diverse, which is an important problem that needs to be overcome in membrane applications. In this paper, three foulant systems consisting of humic acid, humic acid plus Ca2+ and humic acid plus Ca2+ plus yeast were selected to compare membrane fouling processes with different aeration intensities. The aim was to establish the quantitative relationship between membrane fouling rate and shear stress, respectively, in a large-scale flat sheet MBR (FSMBR). The shear stress values at different aeration intensities were obtained using computational fluid dynamics (CFD). The membrane fouling rate during the filtration of different substances was measured by performing experiments. The comparison results showed that the membrane fouling rate varied greatly during the filtration of different substances. With the help of particle size distribution, the effect of different shear forces on floc size was further explored. Using the dual control of fouling rate and floc size, the recommended aeration intensity was 6~8 L/(m2·min).

Evaluation of a Novel Cuboid Hollow Fiber Hemodialyzer Design Using Computational Fluid Dynamics

Conventional hollow fiber hemodialyzers have a cylindrical shell-and-tube design. Due to their circular cross-section and radial flow distribution and collection in the headers, the flow of blood in the header as well as in the hollow fiber membranes is non-uniform. The creation of high shear stress and high shear rate zones or stagnation zones could result in problems, such as cell lysis and blood clotting. In this paper, a novel cuboid hemodialyzer design is proposed as an alternative to the conventional cylindrical hemodialyzer. The primary motivation behind the proposed design is to create uniform flow conditions and thereby minimize some of the above-mentioned adverse effects. The most salient feature of the proposed design is a cuboid shell within which the hollow fiber membrane bundle is potted. The lumen of the fibers is fed from one side using a flow distributor consisting of embedded primary and secondary channels, while the fibers are drained from the other side using a flow collector, which also has embedded primary and secondary channels. The flow characteristics of the lumen side of the cuboid hemodialyzer were compared with those of a conventional hemodialyzer based on computational fluid dynamics (CFD) simulations. The results of CFD simulations clearly indicated that the flow of liquid within the cuboid dialyzer was significantly more uniform. Consequently, the shear rate and shear stress were also more uniform. By adopting this new design, some of the problems associated with the conventional hemodialyzer design could potentially be addressed.

Removal of Dyes and Cd2+ in Water by Kaolin/Calcium Alginate Filtration Membrane

Kaolin/calcium alginate (kaolin/CaAlg) free-standing membranes were prepared by adding different amounts of Kaolin into the sodium alginate (NaAlg) casting solution and crosslinked by Ca2+ using urea as porogen agent. The morphology of the kaolin/CaAlg filtration membrane was characterized by scanning electron microscope (SEM). Then the kaolin/CaAlg membrane was used for the removal of dyes and Cd2+. The kaolin significantly improved the mechanical behavior and flux of the kaolin/CaAlg membrane. The flux reached 17.53 L/m2·h at 0.1 MPa and when the content of Kaolin in NaAlg was 70 wt.%. The filtration of BSA solution and oil-water emulsion indicated that the kaolin/CaAlg composite filtration membrane exhibited good anti-fouling properties. The rejection of Brilliant Blue G250, Congo red, and methylene blue by the kaolin/CaAlg filtration membrane was 100%, 95.22%, and 62.86%, respectively. The removal rate of Cd2+ reached 99.69%, with a flux of 17.06 L/m2·h at 0.1 MPa.

Bisection method for accurate modeling and simulation of fouling in hollow fiber membrane system

Accurate description and modeling of fouling on hollow fibers imposes a serious challenge to more effective fouling mitigation and performance optimization of the membrane system. Although the governing equations for membrane fouling can be constructed based on the known theories from membrane filtration and fluid dynamics, they are unsolvable analytically due to the complex spatially and temporally varying nature of fouling on hollow fibers. The current available numerical solutions for the governing equations are either unreliable or inconvenient to use because of the uses of unfounded assumptions or cumbersome calculation methods. This work presented for the first time a rigorous numerical procedure to solve the governing equations for fouling development on hollow fibers. A critical step to achieve the goal is the use of bisection method to determine the transmembrane pressure at the dead end of the fibers. With this procedure, fouling behavior in the hollow fiber membrane system under a given condition can be simulated within a second. The model simulations were well calibrated and verified with the published experimental data from literature. Also presented in the paper were simulations for performances of the hollow fiber membrane system under various operation conditions. Graphical abstract ᅟ.